Over the last 15 years, a number of fiber optic components and devices such as: couplers, attenuators, wavelength division multiplexers/demultiplexers, connectors, filters, switches, fiber-pigtailed semiconductor lasers, isolators, etc., have been developed for use in fiber optic communication systems, sensors and instrumentation. In nearly all of these applications employing fiber optic components or devices, design-specific mounting fixtures are utilized to precisely align, position or secure optical fibers or elements within such optical fiber components or devices. In most of these applications, it is common for such mounting fixtures to be formed of a fused silica material because its low coefficient of thermal expansion closely matches that of the optical fibers and other optical components or devices. In this respect, maintaining the stability and relative position of optical fibers, components or devices, through the correct choice of materials, is particularly critical in that even minor relative movements between such elements may result in large variations or degradation in optical characteristics, such as coupling ratios and insertion losses.
Optical fibers, components and devices are typically secured to a base plate or substrate with an epoxy material. The two most common types of epoxy adhesives used in these applications cure upon exposure to either UV light or heat. The epoxy adhesives are widely used because they are inexpensive, easy to use and in many instances, readily cured. Rapid in-situ cure schedules are also well suited for volume manufacturing.
While epoxies offer a convenient means for attaching optical fibers, components or devices to substrates or to other optical fibers, components or devices, the physical properties of cured epoxies often make such materials less than ideally suited for use in fiber optic systems. In one respect, epoxies typically possess very different coefficients of thermal expansion relative to the optical fibers, mounting substrates, optical components and devices they are used to secure. This difference may affect the stability and relative position of the respective components or devices when exposed to temperature changes. In another respect, epoxies have a tendency to absorb moisture. Such tendency is detrimental in that moisture significantly reduces an epoxy's ability to firmly secure the optical fiber, optical components or devices to other optical fibers, components or devices or to a substrate. In addition, the cured epoxy swells as it absorbs water vapor, and this swelling may strain the relative attachment between optical fibers, or optical components, or optical devices, or the supporting substrates. In general, moisture induced swelling and subsequent degradation of the epoxy adhesive may cause misalignment or even detachment of the optical fibers, components or devices relative to a supporting substrate or other optical elements. Additionally, epoxies exhibit physical degradation from prolonged exposure to environmental conditions, such as thermal, oxidative and photo degradation which may cause a further breakdown of the epoxy structure over such periods of exposure.
As fiber optics continue to penetrate the telecommunications market, product lifetimes of 20 years or more will be mandatory. In order to achieve this degree of performance, new packaging techniques and materials, other than epoxies, will be required for reliably attaching optical fibers, components or devices to supporting substrates and to each other. Ceramic based cements or adhesives may be used in some applications as an alternative to epoxies since these materials are particularly impervious to moisture. One major disadvantage associated with their use, however, is that they require long cure schedules, often at elevated temperatures, which for example, substantially hinder their usefulness in high volume production.
A large variety of glass powders, commonly known as glass frits are used for making joints or seals. These materials are used for making strong, insulating and often hermetic connections between different materials such as glass, ceramics or metals. Due to the inorganic nature of these materials, these materials are particularly impervious to moisture. They consist of various metal oxides such as lead, boron and zinc. However, most of these frits exhibit large coefficients of thermal expansion, typically 10 to 100 times larger than that of silica. Furthermore, the use of these frits requires subjecting the assembled article to long annealing schedules in order to prevent the formation of fractures and also temperatures of between 400.degree. C. to 1000.degree. C. are typically required. However, since the acrylate buffer coating on optical fibers is damaged at 150.degree. C., the buffer precludes the use of furnace based techniques traditionally used to soften and anneal such glass materials. This disparity in the coefficients of thermal expansion, in the event a glass frit with a typical coefficient of thermal expansion is used as an attachment material, may result in the occurrence of a stress at the interface between the fused glass frit and the optical fiber, component, device or support substrate. Such stress may be relieved through the formation and propagation of a crack within the fused glass frit or optical fiber, device or component (cohesive failure) or by the separation of the fused glass frit at the glass frit/optical fiber, device or component interface (adhesive failure). Such cohesive or adhesive failure is undesirable.
The present invention overcomes these and other problems and provides an improved method of using a glass composition for securing optical fibers, components and devices to mounting fixtures or to other optical fibers, components or devices, which method of securing creates a bond between such components that is less susceptible to physical degradation from exposure to adverse environmental conditions and that reduces the likelihood of deterioration of the performance of such components as a result of such exposure than bonding procedures known heretofore.